20 August 2009

Global perspectives: Solar plants in Spain boost valve control

By Cris Whetton

The Andasol 1 plant in the Spanish province of Granada is Europe's first parabolic trough power plant and the world's largest solar power plant.

The plant’s 510,000 m2 collector surface area provides a generating capacity of 50MW, enough to meet the annual electricity demand of 50,000 households. The success of Andasol 1 and sister plant Andasol 2 has reinforced the argument for the construction of similar renewable energy plants, many of which are now in progress throughout the world. The parabolic trough is a long parabolic mirror with a Dewar tube running its length at the focal point. Sunlight reflected by the mirror concentrates on the tube. Heat transfer oil flowing through the tube then absorbs the sunlight. The oil heats steam in a conventional turbine generator.

At both Andasol sites, Rotork IQ intelligent electric actuators with Pakscan 2-wire digital control are on order for valve control in all areas of the generating process. Rotork Iberia worked closely with the plants’ engineering company, Sener, to integrate the actuation and control system into the overall plant design. The technology has long-range bus capabilities and can operate a loop up to 20 kilometers long without any deterioration in communication performance or the need for repeaters. This has enabled over 100 actuators at each Andasol site to undergo control and monitoring with a single bus loop. Each loop undergoes supervision by a channel master station, which provides the communication interface with the plant’s control centre. The main pipework circuits on a parabolic trough power plant comprise of the Heat Transfer Fluid thermal oil pipes that carry the heat transfer oil around the mirrors, the steam plant, and the power generation circuits. In addition, a liquid salt heat storage circuit can enable electricity to generate for up to 7½ hours after the sun has set. In all plant areas, on-off valve control is possible using quarter-turn electric actuators.

In Britain, Rotork won contracts worth $1.4 million (€1 million) to supply fluid power and electric valve actuators for a major petrochemical expansion project in the Far East.

The $3 billion Shell project involves modifications to existing facilities and the construction of new petrochemical production plants at two refinery sites that comprise the Shell Eastern Petrochemicals Complex in Singapore. The majority of the Rotork orders are for heavy duty GP and LP range quarter-turn and linear pneumatic actuators manufactured at the Rotork Fluid Systems plant in Lucca, Italy. In addition, Foundation Fieldbus-enabled Rotork IQ and IQT multi-turn and quarter-turn electric actuators are on order from Rotork Controls in the U.K.

Cris Whetton is InTech’s European correspondent.